The invention is directed to a process for the production of 2,3-cycloalkenopyridines by the catalytic reaction of a cycloalkanone or cycloalkenone with an aliphatic oxo compound at elevated temperature. The 2,3-cycloalkenopyridines are important intermediate products for the production of medicines, plant protective agents and synthetic resins.
It is known to produce 2,3-cyclohexenopyridine by the catalytic dehydrogenation of decahydroquinoline (Berichte Vol. 67 (1934) pages 1715 to 1729). The yield is merely 36%. It is already known to produce 2,3-cyclopentenpyridine, 2,3-cyclohexenopyridine and 2,3-cycloheptenopyridine from the corresponding cycloalkanones (Annalen Vol. 478 (1939) pages 176 to 196, Helv. Chem. Acta Vol. 28 (1945) pages 1677 to 1683), in each using 4 intermediate steps. The disadvantage of these processes is that they are very expensive and the highest yield is 40%.
Furthermore, it is known to produce 2,3-cycloalkenopyridine by reaction of cycloalkanones with 3-aminoacroleins in the liquid phase at 120.degree. C. using triethylamine and piperidine acetate as catalyst (Tetrahedron Letters No. 38 (1970) pages 3291 to 3294). This process requires as the starting materials the relatively difficulty accessible aminoacroleins. Besides despite 24 hours reaction time the yields of the desired cycloalkenopyridines are only 30 to 60%.